Also Wednesday, a British soldier died in a roadside bombing in the southern province of Helmand, bringing the number of NATO troops killed in Afghanistan since Sunday to 23. And a suicide bomb attack at an Afghan wedding reception in Kandahar province killed at least 40 people Wednesday night and left nearly 80 wounded, news services reported.

The Air Force Black Hawk helicopter was shot down around noon in the Sangin district, in eastern Helmand, U.S. and Afghan officials said.

A rocket-propelled grenade appears to have downed the craft, said Brig. Gen. Frederick B. Hodges, one of the top U.S. commanders in southern Afghanistan, who cited the findings of a preliminary investigation.

Hodges said NATO aircraft are routinely shot at, but generally without deadly effect because the Taliban appears to lack sophisticated surface-to-air missiles.

"It's a big deal every time we lose someone," he said. "But this is more of a jolt. The medevac crews are some of the bravest people in the world. Just by the nature of what they do, they're always moving into danger."

Three service members survived the crash, Hodges said.

The Taliban asserted responsibility for the attack in a statement that said insurgents fired at the aircraft as it was flying at a low altitude near the market in Sangin.

American helicopters are particularly vulnerable to Taliban attacks when operating in areas such as Sangin, where there are relatively few U.S. and NATO forces. In many of the remote valleys of eastern Afghanistan with a light U.S. presence, earlier Taliban shoot-downs of Chinooks and Black Hawks forced U.S. commanders to change tactics.

The rocket-propelled grenades and the heavy machine guns that the Taliban has used are fairly crude. To counter them, U.S. helicopter crews entering remote valleys have shifted to flying only at night and only on evenings when there was little moonlight. The restrictions made it harder to reach more isolated U.S. bases but helped to mitigate attacks.

The lack of Taliban surface-to-air capacity has given the United States and other foreign powers a tactical advantage, enabling them to fly at relatively low altitudes over insurgent strongholds in the south and the east. In contrast, the U.S. decision in the 1980s to supply mujaheddin in Afghanistan with Stinger missiles marked one of the major turning points of the Islamic rebels' fight against Soviet forces. Russian aircraft were forced to fly at much higher altitudes or risk being shot down.

The rising death toll comes as the U.S. military is deploying thousands of troops to Helmand and Kandahar provinces in a bid to take Taliban strongholds.

Hodges said the recent casualties have been painful but not surprising. "We had expected the enemy to push back as we have more and more success," he said.